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Biomedical subjects

D Henderson

Publications and source records attributed to D Henderson.

At least 73 records · Page 4Linked to original sources
PubMed1999

Auditory nerve fiber responses following chronic cochlear de-efferentation.

The aim of the present study was to examine the role of the olivocochlear system in auditory processing by examining the long-term effects of cochlear de-efferentation on auditory nerve response properties in adult chinchillas. Spontaneous rates, response thresholds, tuning curves, discharge rate-level functions, and adaptation of single auditory nerve fibers were measured in chinchillas with complete cochlear de-efferentation produced by sectioning the olivocochlear bundle in the internal auditory meatus. De-efferentation was verified as successful on the basis of acetylcholinesterase staining of surface preparations of the organ of Corti. Following chronic de-efferentation, there was a striking decrease in spontaneous rate, consistent with earlier observations in cats. In addition, the present study shows that complete de-efferentation results in: (1) increased driven discharge rates and decreased dynamic range of discharge rate-level functions, (2) larger onset-to-steady state ratio of discharge rate at moderate intensities, and (3) a hypersensitive tail of the tuning curve. These effects, largely confined to neurons that were most sensitive to frequencies between 2-8 kHz, indicate that the cochlear efferent system is important in maintaining normal function (e.g., frequency and intensity selectivity) of the auditory periphery by modulating auditory nerve fiber response properties.

Acetylcholinesterase↗
PubMed1999

A Molecular Theory of the Hydration Force in an Electrolyte Solution.

A model, consisting of a pair of large macroions in a dipolar hard sphere-point ion electrolyte, is considered in order to evaluate the hydration force (solvent-mediated) contribution to the force between colloidal particles, which is missing in the DLVO theory. Using the mean spherical approximation (MSA), an explicit expression for this force is obtained. It is shown that the force consists of the hard-core exclusion term that was proposed recently by Henderson and Lozada-Cassou (HLC) [J. Colloid Interface Sci. 121, 486 (1988)], and a dipole alignment contribution that originates from the orientational ordering of the solvent molecules near the colloidal particles. The long-range asymptotic form of the total force is given by a Coulomb contribution and is described by the Poisson-Boltzmann or Derjaguin-Landau-Verwey-Overbeek (DLVO) result. The hydration force is short-ranged and extends about ten solvent layers and is responsible for the oscillations of the total force. The total force that we obtain is similar to the semiempirical result of HLC. The comparison with the experimental results for a 10(-3) M KCl electrolyte solution is discussed. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Self-aggregation of DNA oligomers with XGG trinucleotide repeats: kinetic and atomic force microscopy measurements.

Turbidity measurements via absorbance monitoring at 320 nm were employed to obtain autocatalytic-like kinetic profiles of K+-induced aggregate formation of d(XGG)4 and some related oligomers, where X = A, C, G, and T. At least 1 M KCl is needed to observe the turbidity-measurable aggregation at pH 8, and the relative propensity for aggregate formation is shown to follow the order d(GGG)4 > d(AGG)4 approximately d(TGG)4 >> d(CGG)4. The presence of Mg2+ greatly facilitates and dramatically reduces the amount of K+ required to initiate aggregation and significantly enhances the thermal stabilities of the aggregates. Replacement of K+ by Na+ fails to induce a similar phenomenon. The Psi-type CD characteristics of aggregates are strongly dependent on the sequence and ionic conditions. Despite their ease of aggregate formation, oligomers with AGG trinucleotide repeats fail to exhibit Psi-CD formation. The propensity for aggregation is greatly affected by the chain length, with oligomers of four repeats being most facile. Appending X base at the 3' end of d(GGXGGXGGXGG) appears to provide a greater hindrance to aggregation than at the 5' end. Atomic force microscopic images support some of these findings and reveal the morphologies of these aggregates. The presence of MgCl2 in solutions appears to considerably elongate the K+-induced aggregates.

Circular Dichroism↗
PubMed1999

Priorities for research in Emergency Medical Services for Children: results of a consensus conference. EMSC Research Agenda Consensus Committee, National EMSC Resource Alliance.

STUDY OBJECTIVE: The study objective was to arrive at a consensus on the priorities for future research in Emergency Medical Services for Children (EMSC). METHODS: A consensus group was convened using the Rand'-UCLA Consensus Process. The group took part in a 3-phase process. Phase I involved reviewing a compendium of relevant research articles and answering a mailed questionnaire. Panel members were asked to prioritize topics based on the 1993 Institute of Medicine Report on Emergency Medical Services for Children. Participants were asked to rate each topic based on the significance of the research and whether the topic would (1) improve general knowledge, (2) change behavior, (3) improve health, (4) decrease the cost of care, or (5) change public policy. A 4-point Likert scale was used. They were also asked in the research would require a multicenter study and if the research were feasible. Round II of the study involved a meeting of the panel, where the results of Round I were discussed and the topics reprioritized. The topics were given a rank order and a final ranking was done in Round III. RESULTS: The panel considered a list of 32 topics and these were combined and reworded to give them more precise meaning. Several new topics were also added. Fifteen topics were given a rank order and placed within the 7 broad categories of the Institute of Medicine report. Clinical aspects of emergency care systems organization, configuration and operation and injury prevention were given high priority rankings. The first 5 topics were very close in point-rank order. CONCLUSION: The panel was able to develop a list of important topics for future research in EMSC that can be used by foundations, governmental agencies, and others in setting a research agenda for EMSC.

Child↗
PubMed1999

bcl2 and v-abl oncogenes cooperate to immortalize murine B cells that secrete antigen specific antibodies.

In this manuscript, a general strategy was designed and used to rapidly test whether any combination(s) of p53, v-abl, bcl2 and ras oncogenes could act cooperatively to immortalize B cells. Here we report that only the combination of v-abl and bcl2 was successful. Splenic B cells from beta galactosidase-immunized mice were stimulated in vitro with lipopolysaccharide and dextran sulphate for 48 h and co-infected with ecotropic A-MuLV (v-abl) and amphotropic pZip-bcl2 (human bcl2) viruses. When inoculated i.p. into naive pristane-primed mice, these B cells generated mesenteric lymphadenopathy, intraperitoneal lymph nodules and ascites in 100% (8/8) of the mice within 36-53 days. The ascites fluid contained 69.5-122 microg/ml IgG and 2.5-13 microg/ml IgM against the immunogen. The ascites cells were passed intraperitoneally up to three times. In all passages, ascites tumors were generated, and the ascites fluid contained beta galactosidase-specific IgG and IgM, indicating that some immunoglobulin secreting B cells had been immortalized. Neither ascites nor tumors were produced when B cells infected with only one of the viruses was injected into the mice. The presence of each oncogene in ascites cells was verified by immunohistochemistry or RT-PCR. This study provides evidence for the cooperativity of an unexpected pair of oncogenes in B cell immortalization.

3T3 Cells↗
PubMed1999

Priorities for research in emergency medical services for children: results of a consensus conference.

STUDY OBJECTIVE: To arrive at a consensus on the priorities for future research in emergency medical services for children. METHODS: A consensus group was convened using the Rand-UCLA Consensus Process. The group took part in a 3-phase process. Round 1 involved reviewing a compendium of relevant research articles and answering a mailed questionnaire. Panel members were asked to prioritize topics on the basis of the 1993 Institute of Medicine Report on Emergency Medical Services for Children. Participants were asked to rate each topic based on the significance of the research, and whether the topic would (1) improve general knowledge, (2) change behavior, (3) improve health, (4) decrease the cost of care, or (5) change public policy. A 4-point Likert scale was used. Participants were also asked if the research would require a multicenter study and if the research were feasible. Round 2 of the study involved a meeting of the panel, where the results of Round 1 were discussed and the topics were reprioritized. The topics were given a rank order and a final ranking was done in Round 3. RESULTS: The panel considered a list of 32 topics; these were combined and reworded to give them more precise meaning. Several new topics were also added. Fifteen topics were given a rank order and placed within the 7 broad categories of the Institute of Medicine report. Clinical aspects of emergency care, systems organization, configuration, and operation and injury prevention were given high priority rankings. The first 5 topics were very close in point-rank order. CONCLUSION: The panel was able to develop a list of important topics for future research in emergency medical services for children that can be used by foundations, governmental agencies, and others in setting a research agenda for such services.

Child↗
PubMed1999

Intracochlear infusion of buthionine sulfoximine potentiates carboplatin ototoxicity in the chinchilla.

The aim of this experiment was to determine if buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, enhances the ototoxicity of carboplatin. Osmotic pumps were used to infuse BSO into the right cochleas of 12 adult chinchillas for 14 days. The left cochleas served as controls. Animals were assigned to three groups: a drug control group that did not receive carboplatin, a group that received a single dose of carboplatin (25 mg/kg i.p.), and a group that received a double dose of carboplatin (25 mg/kg i.p. x 2), with 4 days between injections. Carboplatin was administered after three days of BSO pre-treatment. Ototoxicity was assessed with evoked potentials recorded from electrodes implanted in the inferior colliculi (ICPs), distortion product otoacoustic emissions (DPOAEs), and cochleograms. BSO infusion itself caused no long-term functional or morphological changes. One of four animals treated with it single dose of carboplatin showed a significant loss of inner hair cells (IHCs), with greater loss in the BSO-treated ear. All animals in the double-dose carboplatin group showed marked differences between BSO-treated and control ears. Average IHC losses were 59% in BSO-treated ears vs. 18% in control ears. Moreover, BSO-treated ears sustained significantly greater outer hair cell (OHC) losses than control ears (37% vs. 2%, respectively). ICP and DPOAE response amplitudes were reduced slightly in BSO-treated ears relative to control ears, consistent with their greater hair cell loss. The results clearly show that BSO can enhance carboplatin ototoxicity in the chinchilla, supporting a role of GSH and reactive oxygen species in platinum ototoxicity.

Animals↗
PubMed1999

"Patient was hit in the face by a fist..." a discourse analysis of male violence against women.

A discourse analysis of professional and popular literature describing male violence against women surveyed 165 abstracts and 11 full-length articles. The phrase "male violence" was used only eight times in these writings; male gender was infrequently mentioned, whereas female gender was often present in the identification of victims of male violence. Consequences of the absence of men as perpetrators and visibility of women in the literature on male violence against women are discussed, and change in these discursive practices is called for.

Cultural Characteristics↗
PubMed1999

Priorities for research in emergency medical services for children: results of a consensus conference.

OBJECTIVE: To arrive at a consensus on the priorities for future research in emergency medical services for children. METHODS: A consensus group was convened using the Rand-UCLA Consensus Process. The group took part in a 3-phase process. Round I involved reviewing a compendium of relevant research articles and answering a mailed questionnaire. Panel members were asked to prioritize topics on the basis of the 1993 Institute of Medicine Report on Emergency Medical Services for Children. Participants were asked to rate each topic based on the significance of the research, and whether the topic would (1) improve general knowledge (2), change behavior (3), improve health (4), decrease the cost of care, or (5) change public policy. A 4-point Likert scale was used. Participants were also asked if the research would require a multicenter study and if the research were feasible. Round II of the study involved a meeting of the panel, where the results of Round I were discussed and the topics were reprioritized. The topics were given a rank order and a final ranking was done in Round III. RESULTS: The panel considered a list of 32 topics; these were combined and reworded to give them more precise meaning. Several new topics were also added. Fifteen topics were given a rank order and placed within the 7 broad categories of the Institute of Medicine report. Clinical aspects of emergency care, systems organization, configuration, and operation and injury prevention were given high priority rankings. The first 5 topics were very close in point-rank order. CONCLUSION: The panel was able to develop a list of important topics for future research in emergency medical services for children that can be used by foundations, governmental agencies, and others in setting research agenda for such services.

Child↗
PubMed1999

Epidemiological study of paratuberculosis in wild rabbits in Scotland.

A survey of 22 farms confirmed the presence of paratuberculosis in wild rabbits in Scotland. Regional differences were apparent in the prevalence of the disease in rabbits, with a significantly higher incidence occurring in the Tayside region. Statistical analysis showed a significant relationship between a previous history or current problem of paratuberculosis in cattle and the presence of paratuberculosis in rabbits on the farms. Molecular genetic typing techniques could not discriminate between selected rabbit and cattle isolates from the same or different farms, suggesting that the same strain may infect and cause disease in both species and that interspecies transmission may occur. The possibility of interspecies transmission and the involvement of wildlife in the epidemiology of paratuberculosis have important implications for the control of the disease.

Animals↗
PubMed1998

Faster recovery in central than in peripheral auditory system following a reversible cochlear deafferentation.

Included among the exciting findings in auditory neuroscience are (i) central plasticity after peripheral injury and (ii) regeneration of auditory nerve fibres following excitotoxic damage. The present study extends our understanding of auditory system plasticity by examining changes in peripheral and central physiology as the cochlea recovers from temporary deafferentation due to excitotoxicity. Application of kainic acid (60 mM) to the round window membrane substantially depressed responses from both auditory nerve and brain stem (inferior colliculus), without affecting distortion-product otoacoustic emissions from the inner ear. The auditory nerve input/output functions recovered over a 30-day period whereas recovery of brainstem response amplitudes occurred within five days. In contrast to amplitudes, thresholds at both peripheral and central levels recovered simultaneously, within five days after kainic acid application. The results indicate that (i) cochlear afferent neurons can recover after excitotoxic damage; (ii) response threshold itself, either central or peripheral, is not sufficient to assess the integrity of the auditory periphery; (iii) the central auditory system can recover more rapidly than the periphery; and (iv) the system can maintain its function in the normal range as peripheral function continues to improve.

Action Potentials↗
PubMed1998

Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla.

Exposure to low level noise prior to a high level exposure reduces noise-induced hearing loss in mammals. This phenomenon is known as sound conditioning or 'toughening'. Reactive oxygen intermediates have been implicated in noise-induced cochlear damage. To evaluate if in situ antioxidant processes may play a role in the toughening phenomenon initiated by low level noise exposure we analyzed glutathione reductase, gamma-glutamyl cysteine synthetase, and catalase in stria vascularis and organ of Corti fractions from cochleae of chinchillas exposed to a sound conditioning paradigm. Chinchillas were either (A) kept in quiet cages (control), (B) exposed to conditioning noise of a 0.5 kHz octave band (90 dB for 6 h/day for 10 days), (C) exposed to high level noise (105 dB for 4 h) or (D) exposed to conditioning noise (B) followed by exposure to the higher level noise (C). Each of the noise exposure conditions (B, C, D) induced changes in the levels of these three antioxidant enzymes. The enzyme-specific activity data for the four subject groups support the following two hypotheses. (1) Changes in glutathione reductase, gamma-glutamyl cysteine synthetase, and catalase play a role in attenuating hearing loss associated with sound conditioning followed by high level noise. (2) Hair cells in the organ of Corti are protected from noise-induced damage by increasing stria vascularis levels of catalase, a hydrogen peroxide scavenging enzyme, and of enzymes involved in maintaining glutathione in the reduced state. The model formulated by these hypotheses suggests that agents that protect or augment the glutathione system in the cochlea may be protective against noise-induced hearing loss.

Acoustic Stimulation↗
PubMed1998

Neutrophil adhesion molecules in HIV disease.

Neutrophil dysfunction in HIV disease is well described. We examined the expression of neutrophil adhesion molecules amongst 72 HIV-infected subjects using a whole blood flow cytometric assay with FITC- and R-PE-labelled isotype-specific MoAbs. We report lesser expression of CD11a (LFA-1) and L-selectin (CD62L) on the circulating neutrophils of HIV+ subjects compared with HIV- controls. Expression of CD11b (Mac-1) was unchanged. Shedding of L-selectin and up-regulation of CD11b in response to in vitro stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) were less in HIV+ compared with HIV- subjects, most markedly in subjects with CD4 cell counts < 100 cells/mm3. These results suggest that neutrophil dysfunction in HIV disease, which increases with disease progression, may be attributable to dysregulated adhesion molecule expression.

Adult↗